1. Field of the Invention
The present invention relates to an electron beam deflecting apparatus having electromagnetic windings for deflecting an electron beam.
2. Description of the Related Art
An electron beam having an energy of about 5 to 50 keV is irradiated onto a resist layer coated on a mask substrate or wafer, and as a result, chemical reaction occurs in the resist layer to obtain a desired pattern of the resist layer. Since such an electron beam has a small radius of less than 0.1 .mu.m, a scanning electron beam exposure system can be of a high resolution type. Also, since the electron beam can be deflected by a magnetic field and an electric field controlled by a computer, the scanning electron beam system is used to enhance the throughput of a lithography process of manufacturing super large scale integrated (LSI) circuits which are highly integrated and extremely precise.
In the above-mentioned scanning electron beam exposure system, the electron beam is deflected by a magnetic field generated from an electromagnetic deflection unit as well as an electric field generated from an electrostatic deflection unit. In the electromagnetic deflection unit where a desired current waveform is supplied to external windings, the circuit configuration therefor is simple, and the focus blur and the scanning distortion are superior as compared with the electrostatic deflection unit. Contrary to this, in the electrostatic deflection unit, energy required for deflection is small and the frequency charactersistics are excellent; however, the deflection voltage may be so large that high insulating and duration characteristics of the circuit configuration are required, and also, it is difficult to generate a desired voltage waveform. Thus, in general, the electromagnetic deflection unit is used for main deflection control, and the electrostatic deflection unit is used for sub deflection control for correcting errors and aberrations.
In a prior art electron beam deflecting method for an electromagnetic deflection unit and a driver for driving the electromagnetic deflection unit, the driver drives the electromagnetic deflection unit directly in accordance with a main deflection amount regardless of its previous main deflection amount. This will be explained later in detail.
In the above-mentioned prior art electron beam deflecting method, however, when the difference between the current main deflection amount and the previous main deflection amount is large, a settling time period in which the electron beam reaches approximately its target position is so large that the exposure time period becomes large.
In another prior art electron beam deflecting method, a deflection amount per one time is limited to smooth the motion of the electron beam (see JP-A-SHO64-27150). This also will be explained later in detail.
In the above-mentioned other prior art electron beam deflecting method, however, the reduction of the settling time period cannot be actually expected, and also, even a waste of time occurs particularly in the case of a low pattern density.
In a prior art electron beam deflecting apparatus, a differentiator is provided for detecting a differential value of a current flowing through the electromagnetic deflection unit, and this differential value is fed back to an electrostatic deflection unit, to thereby reduce the settling time period of the electromagnetic deflection unit (see Y. Takahashi et al., "Electron beam lithography system with new correction techniques", J. Vac. Sci. Technol. B 10(6), pp. 2794-2798, November/December 1992). This will be explained later in detail.
In the above-mentioned prior art electron beam deflecting apparatus, however, since the operation of the differentiator requires time, the exposure time becomes longer.